help

There are LOTS of differing opinions on water changes.....

We do 15ish% every month or so. (so for you that would be roughly 10 gallons.)

I do 10% on my aquariums weekly (ideally.)  However, if you need to lower nitrates, make sure your source water is low in nitrates first (RO/DI with very low TDS).  Adequate live rock (not just size...but you'll need a few big pieces to get an anaerobic zone that can reduce nitrates) will also help.  A deep sandbed (required depth depends on sand particle size) will help too. 

Im no expert but IMO water changes need to be done based upon water quality, in a well established tank once a month should be just fine. In a newer tank, or when you notice your params are out of normal range a weekly or biweekly is recommended. I myself do a 10% water change every 2 weeks on all my tanks (becuase im lazy and rely on my new saltwater to replace all the calc and mag).

With Salt water or you will lower your salinity too much. Top off water is only RO water as the salt does not evaporate with the water.
I try to do 10% a week also but it usually is about every two weeks and on my system right now that I moved about a month ago I haven't changed any water yet...

I also shoot for 10% every week.  The tank thrives and looks much better with routine waterchanges.